David Hall: At 1,314,709 distributed coins, the Stone Mountain half dollar has the second highest mintage of any commemorative of the 1892-1954 classic era (only the 1893 Columbian is higher). The issue was heavily promoted by the Stone Mountain Confederate Monumental Association though various marketing schemes. The original issue price was $1 per coin.
Today, the Stone Mountain is one of the more available commemoratives. Like most of the pre-1933 issues (and unlike the 1933 and later issues), the Stone Mountain is found in circulated grades. But most of the survivors are mint state, including a fair number of Gems. Stone Mountains are usually relatively mark-free. The issue with this coin is toning, eye appeal, and luster, and these three components are all over the place with Stone Mountains. Luster, when it is good, is usually of the frosty variety. Toning and eye appeal run the entire spectrum from gorgeous to downright ugly.
Some Stone Mountain Half Dollars bear counterstamps with state abbreviations, numbers, and/or the letters G.L. and S.L. (for example AR 18 SL). According to Steve Deitert, ". . .every town with a coin quota was designated as a 'unit.' Each unit was entitled to 'at least one coin showing on the face the State initials and a serial number.' (Likewise, special coins could be set aside and numbered for a 'Civic or Patriotic body.') The numbered coins were distributed to the unit chairmen by the Stone Mountain Monumental Association through the governor of each state. Under the governor's direction, 'an alphabetically arranged list of all Units in the State shall be prepared and at some prearranged time and place a drawing for the purpose of determining the place, to which the numbered coins are to be sent shall be held. The coins are to be placed in a receptacle and drawn by a disinterested person, the first coin drawn going to the first Unit town on the list, the second to the second, etc., until all coins are drawn.' The number assigned to each municipality was just the luck of the draw. Each unit chairman then determined when and-where to auction the numbered coin(s)."
The GL and SL designations stood for Gold Lavalier and Silver Lavalier, respectively. These special coins were given to young ladies who sold the most Stone Mountain Half Dollars in their county.
 A. Steve Deitert, "Unraveling the Mystery of the Counterstamped Half Dollar," The Numismatist 124, no. 1 (January 2011), 37-39.